The use of mixed resin beads, which contain a supply of cationic resin beads and a supply of anionic resin beads, for the removal of impurities from water is well-known. In power plants, for example, where vast quantities of water are recycled through a power generating unit containing a steam generator, a condenser, and a circulating system, mixed bed resin demineralizers or polishers are used to remove impurities that are picked up by the recirculating water so as to reduce or prevent corrosion to the components of the system by such impurities. Such mixed resin beds may also be used to purify make-up plant water.
Mixed bed polishers, which normally are provided in such power plant systems to remove impurities from the condensate discharged from a condenser, contain both cationic and anionic resin beads in a common polisher unit. A plurality of the mixed bed polishers are normally provided so that when the resin components of one mixed bed become saturated, that bed can be removed from operation so the beads can be regenerated, while the flow through the power plant system can continue through an alternate bed.
In order to regenerate the beads contained in a mixed resin bed, the cationic bead component must be treated separately from the anionic bead component. The cationic bead resin, for example, might be regenerated by contact with an acidic compound such as sulfuric acid, while the anionic bead resin might be regenerated by contact with a basic compound such as sodium hydroxide.
While, as previously discussed, the cationic beads are generally more dense than the anionic beads and gravity separation can be effected to an extent, a mixture of the bead components will tend to remain at the interface of the cationic bead and anionic bead components of the bed, and complete separation is extremely difficult. The presence of one of the bead components in the other bead component during regeneration results in release of undesirable impurities in the resin bed after it has been returned to service and inefficient operation of the mixed bed.
Attempts have previously been made to provide a process for the complete and efficient separation of the resin bead components of a mixed resin bed so that regeneration of each component can be readily, efficiently and economically effected. In "New Approach of Resin Separation in Condensate Polisher Application", James Y. Chen and James Nichols, presented at the Proceedings 43rd International Water Conference, Pittsburgh, Pa., Oct. 25-27, 1982, pp. 21-31, the problems associated with separation of cationic resin beads from anionic resin beads, from a mixed resin bed are discussed, and methods of separation are described which use optimum density and particle sizes for the cation and anion resins, use inert resin beads with specially sized macroporous resins, and use high concentration caustic soda to separate anion resin beads and particles from cation beads and particles by floatation of the lighter anion resin after primary separation is completed.
It is an object of the present invention to provide a mixed resin bed which contains resin bead components that are easily separable from each other.
It is another object of the present invention to provide an improved process for separating a cationic bead component from an anionic bead component, where both bead components are contained in a resin bed.